KR810002135B1 - The method of reflected wave elimination - Google Patents

Abstract

The method for preventing an ghost phenomenon owing to the intermix of the reflective wave in a TV receiver, is disclosed. In a negative-feedback amplifier, output signal is time-delayed more than one-wavelength of its signal frequency and is attenuated at the constant rate and is feedbacked by the time-delayed attenuating feedback cct. This method can be adapted for microwave and data communications as well as TV receiver.

Description

How to remove TV echo

1a and b: Block diagram showing the method of the present invention.

2-4: An embodiment of the present invention.

The present invention relates to a method of preventing multiple phases from being generated on a television screen by mixing television waves with reflection waves (reflections due to impedance mismatch in a circuit and reflections generated by reflections on buildings and mountains while reaching the antenna).

Conventionally, there is a method of removing reflected waves by using a highly directional antenna or mixing signals of two antennas by using a separate reflected wave removing antenna so as not to receive other than the required fundamental wave, and generating reflected waves reflected from the circuit itself. In order to eliminate the problem, a method of thoroughly matching impedance was used.

The present invention is a completely different method from the prior art by separating and removing the reflected wave from the radio wave itself in which the reflected wave is mixed to prevent the generation of multiple images on the television screen and the detailed description is as follows.

1 is a block diagram illustrating the method of the present invention. A is the amplification degree of the amplifier, K is the feedback rate of the negative feedback circuit, T is the delay time of the delay circuit, and β is the feedback rate through the delay circuit. If the input signal voltage e _i , the output signal voltage e _o , the feedback signal voltage through the negative feedback circuit e _k , and the feedback signal voltage through the delay circuit e e _T , the input and output shown in the block diagram of FIG. The relation with is given by the expression (1).

[e _i -e _T -e _K ] x A = e _O. … … … … … … … … … … … … … (One)

If the fundamental wave of a television radio wave (waves without reflection wave mixing, such as a radio wave transmitted from a broadcasting station) is set to V _ε ^jwt , the reflected wave of the radio wave will change its wave strength ＂V＂ and time ＂t＂, and arbitrary reflected waves. ^{Will be} K ₁ V _ε ^{jw (t-t1)} , K ₂₂ V _ε jw (tt ₂ ), K ₃ Vεjw (tt ₃ ), K _n Vεjw (tt _n ), and so on.

Considering the case where only one reflected wave is mixed, the input signal voltage is ei

ei = Vεjwt + K ₁ Vεjw (tt ₁ ). … … … … … … … … … … … … … (2)

It becomes like (2).

Suppose only the fundamental wave with the reflected wave removed as output

e _O = A'V? jwt... … … … … … … … … … … … … … (3)

The output signal voltage is as shown in equation (3). Where A 'is the transfer function of the negative feedback amplifier. From this assumption, e _K and e _T are as follows.

e _K = KA'Vεjwt... … … … … … … … … … … … … … (4)

e _T = β A 'Vεjw (tT)... … … … … … … … … … … … … … (5)

Again, substituting equations (2), (3), (4) and (5) into equation (1)

A × [Vεjwt + K ₁ Vεjw (tt ₁ ) -β A'Vεjw (tT) -KA'Vεjwt] = A'Vεjwt... … (6)

In order to become like (6) and to establish (6)

K ₁ Vεjw (tt ₁ ) -β A'Vεjw (tT) = 0. … … … … … … … … … … … … … (7)

AVεjwt-AKA'Vεjwt = A'Vεjwt... … … … … … … … … … … … … … (8)

Equations (7) and (8) must be established.

이 되어야 하고

이 되어야 한다.Hence T = t ₁ ,

Should be

Should be

으로 조정하고 K는 안정동작될 수 있게 설정한 회로에서 동작상태를 시간적으로 검토하면Where t ₁ , K ₁ , and A are amounts already determined in the state of the radio wave and circuit configuration, and T, β, and K can be adjusted to arbitrary values by adjustment, so that by adjusting these amounts (7) and (8 ) Can be established. When (7) and (8) are established, the original equation (3) e _O = A'Vεjwt is established. Now T = t ₁ and

If you check the operation status with the circuit that is set to make stable operation

When starting the circuit operation at t = 0 +, e _i = Vεjwt + K ₁ Vεjw (tt ₁ ),

t is 0 <t <t ₁ when il is the _{e O = A'Vεjwt + K 1 A'Vεjw} (tt 1).

이므로When t is t ₁ <t <2t ₁ , T = t ₁ ,

Because of

e _T = K ₁ Vεjw (tt ₁ ) + K ₁ ² Vεjw (t-2t ₁ )

e _O = A '(e _i -e _T ) = A'Vεjwt-K ₁ ² A'Vεjw (t-2t ₁ )

When t is 2t ₁ <t <3t ₁

e _T = K ₁ Vεjw (tt ₁ ) -K ₁ ³ Vεjw (t-3t ₁ )

e _O = A'Vεjwt + K ₁ ³ A'Vεjw (t-3t ₁ )

Over time (when t is infinitely larger than t ₁ ), K ₁ <1, so the second term is ＂0＂ and only the A'Vεjwt term remains, thus establishing the original assumption.

In this case, the conventional feedback amplifier feeds back a time within one wavelength, but the present method is characterized in that the delay time is at least one cycle (one wavelength pass time) of the input signal. If the reflected wave delayed by a certain time is mixed with the intensity of the radio wave during the input, the reflected signal can be removed by delaying the output signal through the delay circuit and negative feedback to the input side. Even if multiple reflected waves of different time and intensity are mixed on the input side, it can be removed in the same way. However, the proof of formula is omitted since it is almost the same as the case of one reflection wave.

2-4 is an example which comprised the actual circuit by this method. FIG. 2 is an embodiment of the present method for removing the reflected wave when there is only one reflected wave. Referring to the operating state, an input is applied to terminals 1 and 2, and an input voltage is applied across a resistor R _b through a capacitor C _i . The input is applied between emitter E and base B of transistor T _r via coil Lb ₁ ′ and resistor R _E. This signal is amplified by the transistor and output from the collector C through the capacitor C _O to terminals 3 and 4 across the output resistor R _O. The feedback signal attenuated by the attenuator resistor R _T by the coil L ₂ and L _T and the capacitor C _T is delayed by a predetermined time (adjusting the terminal S and finished at a predetermined time), and the coil Lb ₁ is excited. _It is induced at ₁ 'and negatively feedbacked, and the coil terminals are interchanged to adjust polarity. The reflected wave voltage and the voltage of the magnitude across the resistor R _b are induced in the coil Lb _{1 so} that only the fundamental wave of which the reflected wave is canceled is applied between the base and the emitter of the transistor. The coil L _T and the capacitor C _T are known as distribution constant times, and the resistor R _L is for impedance matching. It also adjusts R _E to adjust the current feedback and stabilize the circuit operation. R _g is a resistance for bias.

3 is a circuit in which the occupational resistance is connected without the coil Lb ₁ and the operating state is the same as that of FIG.

4 is an embodiment of the present method for removing a case where four reflected waves are mixed among a plurality of reflected waves on an input side, and the second operation is the same as the second operation, but uses a plurality of time delay negative feedback circuits. The reflection wave is removed by applying the same negative voltage as the respective reflection wave to the coils Lb ₁ ′, Lb ₂ ′, Lb ₃ and Lb ₄ ′, respectively.

As described above, one or more reflected waves included in the input side can be easily removed, thereby making the television image very clear, and the method can be used for microwave communication, data communication, etc. in addition to the television field.

Claims (1)

A known negative amplifier, comprising: at least one time delay attenuation feedback circuit configured to delay an output signal by one or more wavelengths of the signal frequency and attenuate at a predetermined ratio to negatively feedback the input side.

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